1. Field of the Invention
The present invention relates to a system and method for filtering and enhancing signals from a noise background.
2. Brief Description of the Related Art
In linear systems, noise is considered detrimental to signal; in nonlinear systems, the relationship is more complex. While increased intensity leads to wave mixing of the signal components, creating effective noise, nonlinear coupling can lead to an energy exchange in which the signal grows at the expense of the noise. This amplification only holds for certain parameter ranges, e.g. noise and coupling strengths, that give rise to the term “stochastic resonance”. The effect occurs throughout science, from climatic patterns to electrical systems to biology, but mostly in the context of one-dimensional signals that spike above a threshold. For example, many works have focused on neuronal activity in vision but little attention has been paid to the images themselves.
In the past, the stochastic resonance phenomenon has been applied in a variety of systems. For example, in U.S. Pat. No. 5,574,369 entitled “Detection and Communications Device Employing Stochastic Resonance,” Hibbs et al. disclosed a device employing the stochastic resonance phenomenon to perform amplification of a signal by increasing the amplitude of a signal input into the device through the external addition of noise at the input. The central element of the Hibbs et al. system was a super-conducting loop interrupted by one or more Josephson junctions.
Further, in U.S. Pat. No. 6,008,642, entitled “Stochastic Resonance Detector for Weak Signals,” Bulsara et al. disclosed a stochastic resonator signal detector comprising a multi-stable nonlinear device for coupling to an input signal and a control signal coupled to the multi-stable nonlinear device for varying asymmetry among stable states of the multi-stable nonlinear device. The interaction of the input signal with the control signal in the multi-stable nonlinear device generated an output signal having an amplitude responsive to the input signal amplitude and a frequency range that comprised harmonics of products of the control signal and the input signal.
The nonlinear coupling between signal and noise, usually in the context of intensity-dependent clicks of a detector, is a generic problem in information physics. Despite this, the interaction has received little attention in imaging. See, Simonotto, E. et al., “Visual perception of stochastic resonance,” Physical Review Letters 78 (6), 1186-1189 (1997); Vaudelle, F., Gazengel, J., Rivoire, G., Godivier, X., & Chapeau-Blondeau, F., “Stochastic resonance and noise-enhanced transmission of spatial signals in optics: the case of scattering,” Journal of the Optical Society of America B-Optical Physics 15 (11), 2674-2680 (1998).